Abstract
The properties of fetal human brain monoamine oxidase (MAO) was studied and the multiplicity of MAO was also studied on kinetic investigation, substrate specificity and inhibitor sensitivity using clorgyline and deprenyl. MAO activity was measured by radiometric assay using β-phenylethylamine (PEA), benzylamine, serotonine (5-HT) and tyramine as substrates. The MAO activities with all substrates tested were linearly proportional to enzyme volume and reaction time and the optimum pH with all substrates were about 8.5. In fetal human brain, Km value of MAO for PEA was 1.4 μM and was much lower than those for other substrates and Km values of MAO for tyramine, 5-HT and benzylamine were found to be higher than those in postnatal brain. Vmax value and specific activity of MAO for 5-HT were higher than those for PEA and benzylamine. The inhibition curves of MAO by the two inhibitors showed that the MAO-A/ MAO-B ratio was 1.5-3.0 in fetal human brain and the very low activity of benzylamine oxidase (BZAO) which may derive from vascular tissue rather than brain tissue were found using benzylamine as substrate. This result indicates that MAO-A predominates to MAO-B in fetal human brain despite the predominance of MAO-B in postnatal brain.
